This invention relates generally to switching devices used to change the source of an incoming power supply to an electrical load. More particularly, the invention relates to a dedicated transfer switch for use on an electrical load, such as a traffic signal, that allows an alternate power source to be connected to the load when the primary power source is interrupted.
Most electrical devices or loads receive electrical power from a utility, and thus become inoperable when the utility power supply is interrupted for any reason. With some devices or loads, a period of inoperability is tolerable. However, with other devices or loads, it is necessary to provide an alternative means for performing the function of the load or device during the time the load or device is inoperable. For example, when a traffic signal is rendered inoperable due to interruption of its normal power supply, one alternative is to place temporary stop signs at certain comers of an intersection to control traffic flow. Frequently, stop signs are placed at all corners. While this solution controls traffic, it does so in a far less efficient manner than traffic signals. During periods of high traffic volume, a significant amount of congestion can occur at an intersection where this solution is employed during a period of power interruption. Alternatively, a police officer or the like can be positioned at an intersection where a traffic signal is inoperable, so as to direct traffic through the intersection. Again, however, this results in a less than optimal traffic flow through the intersection and requires use of personnel.
While the above solutions are generally satisfactory to control traffic at an uncontrolled intersection during interruption of power to traffic signals, both have significant drawbacks. It is thus desirable to operate traffic signals from an alternate power source when supply of utility power to the traffic signals is interrupted.
In another example, interruption of utility power cuts off the supply of water to all users of a community well. While this is initially an inconvenience, it can become a serious situation if the interruption endures for a long period of time.
It is an object of the present invention to provide an arrangement for supplying power to an electrical device or load, such as a traffic signal or community well, from an alternate power source when the supply of utility power is interrupted. It is a further object of the invention to provide the ability to quickly and efficiently connect an alternate power supply to an electrical device or load. Yet another object of the invention is to provide a power transfer device which is relatively simple and inexpensive, and which is operable to quickly change the source of incoming power to an electrical device or load, such as from a standby generator. A still further object of the invention is to provide a power supply transfer switch which can be placed in any location as desired along the path of incoming power to the load or device.
In accordance with one aspect of the invention, a transfer switch is interconnected in the power supply system for an electrical load or device. The transfer switch includes an input arrangement having a power input receptacle and a selector switch, and is wired into the power supply to the load or device. The selector switch is operable to select the source of power to the load or device, and is also operable to cut off the supply of power to the load or device. During periods of normal operation, the selector switch is set to allow power to be supplied to the load or device from primary or utility power lines which are interconnected with the transfer switch and the load or device. In order to service the load or device, the selector switch is set to a position which cuts off the supply of power to the load or device. When utility power to the load or device is interrupted and it is desired to supply power to the load or device from an alternate source of electrical power, such as a standby generator, a plug associated with a power input cord from the generator is engaged with the power input receptacle to supply input power from the generator to the transfer switch. The selector switch is then positioned so as to supply power to the load or device from the generator, and the load or device can then be operated for as long as desired from the standby generator, typically until utility power to the load or device is restored. In this manner, the only period of interruption in operation of the load or device is the time it takes to connect the standby generator to the load or device, and the load or device can thus be operated in a normal manner with minimal disruption in service.
The transfer switch preferably includes a box-like enclosure having a top wall, a bottom wall, a rear wall, and a pair of sidewalls defining an internal cavity having an open face. A partition is mounted in the internal cavity defined by the enclosure, and divides the internal cavity into an inner portion and an outer portion. The power input receptacle and the selector switch are both mounted on the partition such that the power input receptacle and the selector switch are accessible from the open face of the enclosure. The enclosure further includes a removable cover pivotally connected between open and closed positions relative to the open face by a hinge assembly located between the enclosure and the cover to selectively allow and prevent access to the power input receptacle and the selector switch. The cover includes a latch engageable with a locking mechanism secured on the enclosure opposite the hinge assembly. The power input receptacle and the selector switch are interconnected to the load, the primary power source, the alternate power source and a ground connection on the enclosure by wiring retained in the inner portion of the enclosure. The rear wall of the enclosure is formed with a knock-out opening through which the wiring extends. The bottom wall of the enclosure is provided with a retainer notch allowing a power cord leading from the plug connector to the alternate power source to extend freely from the enclosure when the cover is in the closed position over the outer portion of the enclosure. The partition includes an upper angled positioning plate having a mounting portion and a lower angled positioning plate connected thereto. The power input receptacle extends through and is fixed to mounting portion of the partition. The power input receptacle includes a cylindrical body and a circular collar extending generally perpendicularly to the body at one end thereof and overlying the mounting portion of the partition. The power input receptacle further includes a recessed end wall spaced from the collar for mounting a set of male prongs receivable in the plug connector connected to the alternate power source. The selector switch is connected to an incoming primary power supply wire and an incoming alternate power supply wire from the power input receptacle, and to an outgoing power supply wire from the selector switch leading to the load. The selector switch is selectively connectable to either incoming power supply wire. The selector switch includes a rotatable handle selectively engageable in first and second positions with the incoming power supply wires to define closed electrical circuits with the desired power source, and selectively engageable in a third position to disconnect the load from either of the incoming power supply wires.
In the preferred embodiment, the load is a traffic signal, and the enclosure is mounted on or in a control box positioned between the traffic signal and the primary power source. The enclosure may also be mounted on a support device located adjacent the traffic signal, or at any point desired along the path of the power supply to the traffic signal.
In another aspect of the invention, a transfer switch is connected to an electrical traffic signal for switching power from an electrical utility source to a generator power source in the event of an interruption in the electrical utility source. The transfer switch includes an enclosure operably connected to the traffic signal and having a power input receptacle for selectively receiving the generator power source and supplying generator power to the traffic signal, and a selector switch cooperable with the power input receptacle for selecting the source of electrical power to the traffic signal and effecting a cut off in the supply of power to the traffic signal.
The invention also relates to a method of providing a transfer of power to an electrical load, such as a traffic signal, from an electrical utility power source to a generator power source. The method is carried out by providing an enclosure having an open face, a power input receptacle mounted within the enclosure, and a selector switch mounted in the enclosure adjacent the power input receptacle and having connections with incoming power supply wires from both the electrical utility power source and the generator power source through the power input receptacle, and with an outgoing power supply wire leading to the traffic signal, and a removable cover movably attached to the enclosure for selectively allowing and preventing access to the power input receptacle and the selector switch by moving the cover to open and close the open face. The method further includes removing the cover on the enclosure exposing the power input receptacle and the selector switch; moving the selector switch from a first operative position connecting the incoming power supply wire from the utility power source with the outgoing power supply wire to an OFF position wherein the outgoing power supply wire is disconnected from both incoming power supply wires; inserting a plug leading from the generator power source into the power input receptacle; and moving the selector switch from the OFF position to a second operative position in which the outgoing power supply wire is connected to the incoming power supply wire from the generator power source. The step of removing the cover includes releasing a locking mechanism on an exterior surface of the enclosure which is engageable with a latch attached to the cover, and moving the cover away from the enclosure. The step of moving the selector switch includes rotating a handle located on the selector switch. The step of inserting the plug further includes joining the plug with the power input receptacle and placing a power cord trailing from the plug into a retainer notch formed in a bottom wall of the enclosure. Once the selector switch has been moved to its second operative position, the removable cover is closed on the enclosure and the cover is locked by engaging the latch on the cover with the locking mechanism on the enclosure.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.